The half-tone phase shift mask has been used in the photolithography process having high resolution so as to fabricate a fine contact hole or a fine patterning. Especially, when an i-line exposure equipment is used in the process, a phase shift layer provided to the half-tone phase shift mask is formed of a material such as MoSi, MoSiN or MoSiON that transmits approximately 4.about.12% of light and shifts phase of the light.
FIG. 1 is a cross-sectional view showing a general half-tone phase shift mask.
Referring to FIG. 1, a phase shift layer 13 that transmits approximately 4.about.12% of light and shifts phase of the light by 180.degree., is formed on a quartz substrate 11. The phase shift layer 13 is formed of one selected among MoSi, MoSiN and MoSiON, and with thickness of approximately 1,000.about.1,400A. The phase shift layer 13 is partially patterned so as to act as a contact hole or a pattern mask. At this time, an E-beam writing method is applied to patterning of the phase shift layer 13.
However, as shown in FIG. 2, a bridge 15 occurs as a phase shift layer at an unwanted region during patterning the phase shift layer 13. The bridge 15 is removed by the following methods.
Firstly, the bridge 15 can be removed by a focused ion beam (hereinafter "FIB") method. According to this method, Ga ions (Ga.sup.+) having high energy, i.e. 50.about.100 KeV are implanted to the bridge 15, thereby to drop off the bridge 15 from the quartz substrate 11.
On the other hand, the second repairing method uses a blue laser having long wavelength. A laser having wavelength of approximately 488 nm is applied to the bridge 15, and then the bridge 15 is welded and removed.
However, the following problems occurred in a repair process using the FIB device. Since the FIB repair method is generally applied to Cr mask, it is difficult to remove the bridge made of the phase shift layer having a property of matter, which is different from that of Cr. In other words, the phase shift layer such as MoSi, MoSiN and MoSiON has a stronger bonding force than that of Cr. Therefore, it takes many hours to remove the bridge 15. As a result, referring to FIGS. 4 and 5, residues 15a remain of the bridge 15 and also repair by-products 16 formed around the residue 15a even after a selected time is passed. Herein, the by-products 16 is formed by a reaction between Ga Ions, i.e. ion source of the FIB repair and Si ions, one component of the phase shift layer which comprises the bridge 15 having excellent reactivity with respect to Ga ions. The repair by-products 16 are not easy to remove by the FIB repair method.
Furthermore, if the FIB repair process is performed for a long time to remove the residue 15a of the bridge completely, the Ga ions (Ga.sup.+) having high energy are continuously focused at the quartz substrate 11 of the outside of the bridge 15 or the repair by-products 15a. As shown in FIG. 6, the Ga ions (Ga.sup.+) having high energy are continuously focused on a surface of the quartz substrate 11, thereby pitting some portions (H) of the quartz substrate 11.
Moreover, if the FIB repair process is performed for a long time, the Ga ions (Ga.sup.+) having high energy may permeate inside the quartz substrate 11 with high energy, then the Ga ion (Ga.sup.+) functions as a mask. Therefore, a defect occurs in the pattern on semiconductor substrate.
In the meantime, a method by emitting the blue laser has low accuracy during the repair process since a laser has its inherent characteristic of diffraction. Therefore, edges of repaired portions are removed ununiformly. Thus, if the repaired portions are not removed uniformly, it is difficult to use them as masks for forming a high resolution pattern. Since the phase shift layer as mentioned previously has a strong bonding force, powerful energy and long time are required to remove the bridge by the blue laser.